The invention relates generally to gas turbine engines, and, more specifically, to micro-channel cooling therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. Energy is extracted from the gases in a high pressure turbine (HPT), which powers the compressor, and in a low pressure turbine (LPT), which powers a fan in a turbofan aircraft engine application, or powers an external shaft for marine and industrial applications.
Engine efficiency increases with temperature of combustion gases. However, the combustion gases heat the various components along their flowpath, which in turn requires cooling thereof to achieve an acceptably long engine lifetime. Typically, the hot gas path components are cooled by bleeding air from the compressor. This cooling process reduces engine efficiency, as the bled air is not used in the combustion process.
Gas turbine engine cooling art is mature and includes numerous patents for various aspects of cooling circuits and features in the various hot gas path components. For example, the combustor includes radially outer and inner liners, which require cooling during operation. Turbine nozzles include hollow vanes supported between outer and inner bands, which also require cooling. Turbine rotor blades are hollow and typically include cooling circuits therein, with the blades being surrounded by turbine shrouds, which also require cooling. The hot combustion gases are discharged through an exhaust which may also be lined and suitably cooled.
In all of these exemplary gas turbine engine components, thin walls of high strength superalloy metals are typically used to reduce component weight and minimize the need for cooling thereof. Various cooling circuits and features are tailored for these individual components in their corresponding environments in the engine. For example, a series of internal cooling passages, or serpentines, may be formed in a hot gas path component. A cooling fluid may be provided to the serpentines from a plenum, and the cooling fluid may flow through the passages, cooling the hot gas path component substrate and any associated coatings. However, this cooling strategy typically results in comparatively low heat transfer rates and non-uniform component temperature profiles.
Recently, micro channel cooling has been proposed as a means for improving cooling of critical areas on hot-gas path components. See for example, US Patent Application Publication No. 20120111545 A1, Ronald Scott Bunker et al., “Components with re-entrant shaped cooling channels and methods of manufacture,” which is hereby incorporated by reference herein in its entirety.
Access holes are used to supply micro-channels with coolant from interior spaces within the component. However, FIG. 6 of the present application illustrates a problem associated with forming the access holes. Namely, when abrasive liquid jet (ALJ) drilling is used to make access (coolant supply) holes into the interior cavities 114, once all the ALJ punches through the wall and defines the access hole, the ALJ can also strike the interior surface of the opposite wall, thereby damaging that surface.
It would therefore be desirable to provide an improved process for forming micro-channel cooled components that would prevent or reduce damage to these surfaces during the formation of the access holes used to supply the micro-channels with coolant from the interior of the component.